There are many pipe systems which must be supported in such a manner that the pipes are free to move during normal thermal expansion, but must be restrained from motion during seismic events. Thus, the pipes must be permitted to expand or contract during temperature changes but must be restrained from rapid motion.
In nuclear power generating facilities, for example, numerous pipes carrying various pressurized or high temperature fluids must be supported from the walls or other structure of a building. During normal operation, these pipes must be so supported that they are rigidly secured while still being permitted to expand or contract due to thermal stresses. Also, on shut-down or start-up of such a facility, the pipes will contract or expand to such an extent that they cannot be fixed directly to a supporting structure without provision for thermal effects. While some provision is therefore necessary to permit limited movement of the pipes during thermal changes, which are slow movements, the pipes must be secured rigidly during any possible seismic event so as to prevent rupture of the pipes with the resultant serious consequences. It is thus required that snubbing devices be used in connection with such pipes to enable slow movement, while rigidly securing such pipes during any period of rapid movements.
Such snubbing devices are generally either hydraulic devices or mechanical devices. The hydraulic type of snubbing devices require the use of a hydraulic fluid and various seals which have been found to slowly deteriorate in time, especially when subjected to an environment containing radiation. These hydraulic snubbers thus have high maintenance requirements and servicing is a problem. The use of such hydraulic snubbing devices has therefore given way to various mechanical snubbing devices. Examples of such mechanical snubbing devices are given in U.S. Pat. No. Re 29,221; U.S. Pat. No. 4,054,186; U.S. Pat. No. 4,177,882; and U.S. Pat. No. 4,187,933, which discuss the problems associated with previous hydraulic snubbing devices and which disclose various mechanical means for allowing slow movement of a restrained pipe while preventing rapid movement of the pipes during a seismic event.
The mechanical snubbing devices, while eliminating problems associated with hydraulic devices, pose other problems. For example, because of the mechanical nature of such devices, they are subject to wear and deterioration, and they may also lock up and fail to move so that they must be serviced or replaced. Furthermore, in nuclear power generating facilities, a requirement exists that snubbing devices be periodically operated in order to assure that all snubbers are operating as intended. This requires that each mechanical snubbing device be removed from the installed location and tested through its full operating stroke. Such a procedure is necessarily time consuming and expensive.
An object of the present invention is to provide a snubbing device, that is operable by electronic pulses, which overcomes problems associated with hydraulic and mechanical snubbers.
Another object of the present invention is to provide a snubbing device that is readily tested so as to determine its operability without dismantling or removing the snubber from its location.